A post-mixed burner is a burner in which the fuel and oxidant are injected separately from the burner. The fuel and oxidant mix and react outside the burner. Most industrial furnaces use post-mixed burners.
A number of advantages can be identified using post-mixed burners in which oxidant, comprising pure oxygen or oxygen-enriched air, is supplied to the combustion zone as high velocity jets and the fuel gas is entrained into the oxidant jets. One such advantage is that the burner can be designed to be very flexible because a wide variety of flame patterns are possible. The heat transfer pattern in a furnace can be altered substantially just by changing the oxidant nozzle. Another advantage is that the circulation patterns brought about the high velocity oxidant jets result in uniform heating of the furnace. A third advantage is that the flame can be directed so as to increase the heat transfer rate to the workload. A further advantage is that mixing of the fuel and oxidant is enhanced so as to ensure complete combustion. Yet another advantage is that the formation of nitrogen oxides is reduced with high velocity jets due to the short contact at high flame temperatures within the jet.
A recent significant advance in the field of post-mixed burners is the aspirating burner and method developed by Dr. John E. Anderson which is disclosed and claimed in U.S. Pat. Nos. 4,378,205 and 4,541,796.
There are situations, however, when oxygen or oxygen-enriched air is not readily available at high pressure but is readily available at a lower pressure. One example of such a situation is the waste oxygen from a cryogenic air separation plant for producing nitrogen. In these situations, this oxidant cannot be employed at very high velocity in a combustion process. Therefore, in order to attain the advantages that would have been possible with use of high velocity oxidant, one could attempt to carry out combustion by injecting fuel into the combustion zone as high velocity jets and entraining oxidant into the high velocity fuel jets. The major problem with using high velocity fuel jets is that the combustion flame becomes unstable before a very high velocity can be employed.
It is desirable to have a post-mixed burner and method employing high velocity fuel jets wherein good flame stability is attained.
Accordingly, it is an object of this invention to provide a post-mixed burner and method employing oxygen or oxygen-enriched air as the oxidant wherein the fuel may be injected directly into the furnace zone at high velocity and wherein good flame stability is attained.